SAY it ain’t so. The audience for last Sunday’s debut of season five of “The Sopranos” was apparently smaller than last season.

About 12.1 million viewers tuned in to Sunday’s debut – a huge audience by cable standards.

But the season four debut – back in 2002 – was said to attract 13.4 million viewers, when the debut competed against NFL football.

Still, the audience was bigger than the pay-cable channel’s last big ratings bonanza: the “Sex and the City” series finale three weeks ago which drew 10.6 million viewers.

By HBO’s reckoning, Sunday’s season premiere was the No. 2-rated show of the night – beating all the regular broadcast networks except NBC’s “Law & Order: Criminal Intent” at that hour.

Considering that only about a third of all TV homes subscribed to HBO, network officials say the ratings were a “major accomplishment.”

The lower audience numbers were blamed on a change in the way Nielsen reported ratings. Until last January, ratings for HBO included all six HBO subsidiary channels, which were not showing “The Sopranos.”